In 2022, the two largest international organizations devoted to weight-loss surgery—the American Society for Metabolic and Bariatric Surgery (ASMBS) and the International Federation for the Surgery of Obesity and Metabolic Disorders (IFSO)—joined forces to update the 30-year-old guidelines on who should be considered for metabolic and bariatric surgery (MBS). The new guidelines significantly expand access to care: they recommend surgery for anyone with a body mass index (BMI) of 35 or higher regardless of other health conditions, and they encourage considering surgery for patients with metabolic disease and a BMI between 30 and 34.9. The guidelines also lower BMI thresholds for Asian populations, support surgery in carefully selected children and older adults, and highlight how weight-loss surgery can serve as a bridge to joint replacement, organ transplantation, and improved heart health. All of this is backed by decades of evidence showing that modern weight-loss surgery is safer than ever, with a death rate of just 0.03% to 0.2% around the time of surgery.
Thirty years ago, the National Institutes of Health (NIH) convened a landmark Consensus Development Conference. In 1991, it published a Statement on gastrointestinal surgery for severe obesity, based on expert assessment of the medical knowledge available at the time. That statement addressed surgical treatments for severe obesity, the criteria for selecting patients, the effectiveness and risks of those surgeries, and the need for future research.
The 1991 statement made several important recommendations: nonsurgical programs should be the initial therapy for severe obesity; patients should be carefully selected for surgery after evaluation by a multidisciplinary team; and lifelong medical surveillance should continue after surgery. For the past three decades, the 1991 NIH Consensus Statement has been used by doctors, hospitals, and insurance companies as the standard for deciding who qualifies for bariatric surgery. Under those old rules, a patient needed a BMI of 40 or higher, or a BMI of 35 or higher with obesity-related co-morbidities (additional health conditions caused or worsened by obesity), to be eligible for surgery.
Since that time, hundreds of studies have been published on the worldwide obesity epidemic and global experience with metabolic and bariatric surgery. This research has greatly enhanced our understanding of obesity and its treatment. Obesity is now recognized as a chronic disease, not a personal failing. It is associated with a chronic low-grade inflammatory state and immune dysfunction. Researchers suspect that this prolonged inflammation disrupts the body's homeostatic mechanisms (its internal balance), leading to metabolic disorders commonly associated with obesity through complex pathways involving cytokines, adipokines (hormones released by fat tissue), other hormones, and acute-phase reactants.
Long-term studies published in the decades following the 1991 NIH statement have consistently demonstrated that MBS produces superior weight loss outcomes compared with nonoperative treatments. Multiple studies have also reported significant improvement in metabolic disease and a decrease in overall mortality after surgery, further supporting the importance of this treatment modality. At the same time, the safety of bariatric surgery has been extensively studied. The risk of death in the perioperative period (the time around surgery) is very low, ranging between 0.03% and 0.2%. It is therefore not surprising that MBS has become one of the most commonly performed operations in general surgery worldwide.
The operations themselves have also evolved. The 1991 NIH statement described the vertical banded gastroplasty (VBG) and Roux-en-Y gastric bypass (RYGB) as the dominant procedures. Today, the dominant procedures are sleeve gastrectomy and RYGB, which together account for approximately 90% of all operations performed worldwide. Each has well-studied mid- and long-term outcomes. Other operations still performed include adjustable gastric banding (AGB), biliopancreatic diversion with duodenal switch, and one-anastomosis gastric bypass. The VBG is now of historical interest only and is no longer performed, and the popularity of the AGB has diminished significantly over the past decade. MBS is now preferably performed using minimally invasive surgical approaches (laparoscopic or robotic assisted).
In light of the significant advances in understanding obesity as a disease, its management in general, and metabolic and bariatric surgery specifically, the leaderships of the ASMBS and IFSO convened to produce this joint statement. The guideline represents an evidence-based consensus: the authors reviewed the current available scientific information on metabolic and bariatric surgery, including randomized controlled trials, meta-analyses, large retrospective studies, and prospective databases, and then issued updated recommendations for clinical practice. The statement was published jointly in the journal Surgery for Obesity and Related Diseases in 2022.
Despite its limitations for accurately predicting individual health risk, BMI (body mass index, a measure of weight relative to height) remains the most feasible and widely used criterion to identify and classify patients with overweight or obesity. The new guidelines confirm that MBS is currently the most effective evidence-based treatment for obesity across all BMI classes. Here are the headline changes:
Class I obesity—defined as a BMI between 30 and 34.9 kg/m²—is a well-defined disease that causes or worsens multiple medical and psychological co-morbidities, decreases longevity, and impairs quality of life. The 2022 guidelines state that prospective and large retrospective studies support the notion that MBS should be considered a treatment option for patients with class I obesity who do not achieve substantial or durable weight loss, or meaningful improvement in their co-morbidities, with nonsurgical methods.
Early findings prompted international diabetes organizations to publish a joint statement supporting the consideration of MBS for patients with a BMI below 35 kg/m² and type 2 diabetes (T2D). The evidence base is substantial. Aminian and colleagues summarized data from randomized controlled trials (RCTs), meta-analyses, and observational studies that include individuals with a BMI below 35 kg/m². These data consistently demonstrate the weight loss and metabolic benefits of MBS in individuals with class I obesity.
Specific studies highlight just how strong the evidence is:
It is important to note that medical weight loss is considered to have greater durability in individuals with a BMI below 35 kg/m² than in individuals with a BMI of 35 or higher. Therefore, the guidelines recommend that a trial of nonsurgical therapy be attempted before considering surgical treatment in this group. However, if attempts at treating obesity and obesity-related co-morbidities fail, MBS should be considered for suitable individuals with class I obesity.
The co-morbidities that qualify include:
For patients with a BMI of 35 kg/m² or higher, the evidence is even more definitive. Given the presence of high-quality scientific data on the safety, efficacy, and cost-effectiveness of MBS in improving survival and quality of life in this group, the guidelines state that MBS should be strongly recommended in these patients, regardless of the presence or absence of evident obesity-related co-morbidities.
Why the strong language? Current nonsurgical treatment options for patients with a BMI of 35 or higher are ineffective at achieving the substantial and sustained weight reduction needed to significantly improve their general health. Even in the absence of diagnosed co-morbidities, patients with moderate to severe obesity face threats to their health from physical problems related to excess body weight, undiagnosed obesity-related co-morbidities, the future risk of developing those co-morbidities, and impaired quality of life related to the physical and mental consequences of obesity. In short: the potential harms of staying at a high BMI far outweigh the risks of surgery for most patients.
The World Health Organization (WHO) defines the terms overweight and obesity based on BMI thresholds. The 1991 NIH statement noted that the "risk for morbidity linked with obesity is proportional to the degree of overweight." However, BMI does not account for an individual's sex, age, ethnicity, or fat distribution, and it is recognized as only an approximation of adiposity (body fat).
The guidelines offer a striking example: a patient with a BMI of 30 kg/m² who has visceral and ectopic fat accumulation (fat stored deep in the belly and around organs) with subsequent metabolic and cardiovascular disease would have a significantly higher health risk than a patient with a BMI of 40 kg/m² whose adipose tissue is mainly accumulated in the lower extremities. In other words, where fat is stored matters as much as how much fat there is.
In the Asian population, the prevalence of diabetes and cardiovascular disease is higher at a lower BMI than in the non-Asian population. For this reason, the guidelines state that BMI risk zones should be adjusted to define obesity at a BMI threshold of 25–27.5 kg/m² in this population. Consequently, in certain populations, access to MBS should not be denied solely based on traditional BMI thresholds of 35 or 40.
Coincident with the demonstrated safety of MBS, surgery has been performed successfully in increasingly older patients over the past few decades, including individuals over 70 years of age. In septuagenarians (people in their 70s), MBS is associated with slightly higher rates of postoperative complications compared with younger populations, but it still provides substantial benefits in terms of weight loss and remission of co-morbid disease.
Importantly, the presence of obesity co-morbid disease and the choice of operation are more predictive of 30-day adverse outcomes than age alone. The question of whether there should be an upper chronological age limit is complex. The physiologic changes that occur with aging may impact the effectiveness of MBS, the incidence of postoperative complications, and the ability of older patients to recover from surgery. However, it appears that factors other than age—such as frailty, cognitive capacity, smoking status, and end-organ function—play a more important role.
Frailty, rather than age alone, is independently associated with higher rates of postoperative complications following MBS. Furthermore, when considering MBS in older patients, the risk of surgery should be weighed against the morbidity risk of obesity-related diseases. The bottom line: there is no evidence to support an age limit on patients seeking MBS, but careful selection that includes an assessment of frailty is strongly recommended.
Children and adolescents with obesity carry the burden of the disease and its co-morbidities into adulthood, increasing the individual's risk of premature mortality and complications from obesity-related conditions. The good news is that MBS is safe in the population younger than 18 years and produces durable weight loss with improvement in co-morbid conditions.
The evidence in young patients is compelling:
The American Academy of Pediatrics (AAP) and the ASMBS recommend consideration of MBS in children and adolescents with a BMI above 120% of the 95th percentile (class II obesity) plus a major co-morbidity, or a BMI above 140% of the 95th percentile (class III obesity). Importantly, MBS does not negatively impact pubertal development or linear growth, so a specific Tanner stage (a measure of physical development during puberty) and bone age should not be considered a requirement for surgery. Increasingly, syndromic obesity (obesity linked to genetic syndromes), developmental delay, autism spectrum disorders, or a history of trauma are not considered contraindications to MBS in adolescents.
One of the most valuable roles of weight-loss surgery is helping patients become healthy enough to undergo other life-improving or life-saving procedures. The 2022 guidelines address three specific areas: joint replacement, hernia repair, and organ transplantation.
Poorer outcomes after total joint arthroplasty (complete joint replacement) have been associated with obesity. In fact, some orthopedic surgical societies discourage hip and knee replacement in individuals with a BMI over 40 kg/m². Beyond the technical challenge of performing orthopedic surgery in patients with severe obesity, patients with obesity undergoing joint arthroplasty are at increased risk of hospital readmission and surgical complications, such as wound infection and deep vein thrombosis (blood clots in the deep veins).
There are reports suggesting that MBS may be effective as a bridge to total joint arthroplasty in individuals with class II or III obesity when performed at least 2 years prior to joint surgery. A study of veterans with osteoarthritis demonstrated that an average of 35 months elapsed between MBS and joint arthroplasty or lumbar spine surgery in patients with known osteoarthritis. MBS prior to total knee and hip arthroplasty has been shown to decrease operative time, hospital length of stay, and early postoperative complications. Long-term joint-related complication rates were not significantly different.
One randomized clinical trial is particularly striking. The study enrolled 82 patients with obesity and osteoarthritis: 41 were randomized to receive adjustable gastric banding 12 months prior to total knee arthroplasty (TKA), and 41 were randomized to receive usual nonoperative weight management prior to TKA. At a median follow-up of 2 years after TKA, only 14.6% of patients in the MBS group experienced the primary outcome of composite complications, compared with 36.6% in the control group—a difference of 22%, which was statistically significant (P = .02). This means there is only a 2% probability that this difference was due to random chance. Remarkably, TKA was declined by 29.3% of subjects in the MBS group because their symptoms improved enough after weight loss that they no longer needed the surgery, compared with only 4.9% in the control group.
Obesity is a risk factor for the development of ventral hernias (bulges through the abdominal wall). It increases the risk of impaired wound healing, local and systemic infections, and other complications following hernia repair, and it increases the risk of the hernia coming back (recurrence). Additionally, in addition to a larger volume of subcutaneous soft tissue, abdominal wall hernias in the population with obesity tend to be larger, adding to the complexity of repair.
While the timing of MBS relative to hernia repair remains controversial, evidence suggests that patients with large, chronic abdominal wall hernias may benefit from significant weight loss first, as a staged procedure before definitive hernia repair. The guidelines advise: in patients with severe obesity and an abdominal wall hernia requiring elective repair, MBS should be considered first to induce significant weight loss and consequently reduce the rate of complications associated with hernia repair and increase the durability of the repair.
Class III obesity is associated with end-stage organ disease and may limit a patient's access to transplantation, since obesity is a relative contraindication for solid organ transplantation and poses specific technical challenges during surgery. Conversely, MBS may be overlooked as an option in patients with severe end-stage organ disease. The 2022 guidelines make the case that this is a missed opportunity.
Some patients present special challenges. The 2022 guidelines specifically address three high-risk groups: those with extreme BMI, those with cirrhosis, and those with heart failure.
There is no consensus concerning the best procedure for individuals with especially high BMI, but the efficacy and safety of MBS have been demonstrated in this population. In general, mortality risk increases with increasing BMI, and a BMI above 50 kg/m² has been implicated in increasing surgical risk in older studies. Individuals with a BMI above 60 kg/m² are considered to be at especially high risk for surgery, since these patients have a greater obesity-associated disease burden and more challenging surgical anatomy, resulting in longer operative times, higher rates of perioperative morbidity, and longer hospital lengths of stay in some studies.
However, other studies have failed to demonstrate a significant difference in perioperative complications, length of stay, 30-day mortality, or long-term outcomes after MBS when individuals with a BMI above 60 kg/m² were compared with those below 60 kg/m². Furthermore, studies have shown that MBS can be performed safely in patients with a BMI above 70 kg/m². The guideline concludes that MBS should be considered as a preferred method to achieve clinically significant weight loss in patients with extreme BMI.
Obesity is a significant risk factor for nonalcoholic fatty liver disease (NAFLD), nonalcoholic steatohepatitis (NASH), and the cirrhosis that can follow. At the same time, obesity conveys a 3-fold increase in the risk of liver decompensation (worsening of liver function) in patients with known cirrhosis. The guidelines note that, in addition to inducing significant and durable weight loss, MBS has been associated with histologic improvement of NASH and regression of fibrosis (scarring) in early cases, leading to a reduced risk of hepatocellular carcinoma (the most common type of liver cancer).
Perhaps most impressive: MBS is associated with an 88% risk reduction in the progression of NASH to cirrhosis—meaning that among patients with NASH who undergo weight-loss surgery, the likelihood of developing cirrhosis drops dramatically.
What about patients who already have cirrhosis? The patient with obesity and compensated cirrhosis (cirrhosis that is not causing active symptoms) is
The 2022 ASMBS/IFSO guidelines recommend surgery for anyone with a BMI of 35 or higher, regardless of other health conditions. For those with a BMI between 30 and 34.9, surgery should be considered if they have metabolic disease like type 2 diabetes. Asian populations have lower BMI thresholds, and selected children and older adults may also qualify.
Yes, the new guidelines say surgery should be considered for patients with a BMI between 30 and 34.9 who have metabolic disease such as type 2 diabetes. However, they recommend trying nonsurgical therapy first. If that fails to produce substantial or durable weight loss or improvement in your diabetes, then weight-loss surgery is a suitable option to consider.
For Asian populations, the guidelines adjust BMI thresholds downward. A BMI of 25 or higher suggests clinical obesity, and individuals with a BMI of 27.5 or higher should be offered metabolic and bariatric surgery. This is because Asian populations have a higher risk of diabetes and cardiovascular disease at lower BMIs than non-Asian populations.
Yes, appropriately selected children and adolescents can be considered for surgery. The American Academy of Pediatrics and ASMBS recommend considering surgery for those with a BMI above 120% of the 95th percentile plus a major co-morbidity, or a BMI above 140% of the 95th percentile. Studies show durable weight loss and improvement in co-morbidities in this age group.
There is no evidence to support an upper age limit for weight-loss surgery. Older adults, including those over 70, can have surgery with slightly higher complication rates but still substantial benefits. Factors like frailty, cognitive capacity, smoking, and end-organ function matter more than age alone. Careful selection, including a frailty assessment, is strongly recommended.
Modern weight-loss surgery is safer than ever. The risk of death in the perioperative period—the time around surgery—ranges from 0.03% to 0.2%. The guidelines state that surgery is currently the most effective evidence-based treatment for obesity across all BMI classes. It is one of the most commonly performed operations worldwide.
Yes, surgery can be a bridge to other treatments. For joint replacement, studies show MBS before total knee or hip arthroplasty decreases operative time, hospital stay, and early complications. It can also improve access to kidney, liver, heart, or lung transplant by enabling patients to lose enough weight to become eligible.
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